Electric motors, such as DC (direct current) electric motors utilize carbon brushes in order to supply electrical current to a commutator that is rotatably carried by an armature of the motor. In the past, brushes have been formed to have a rectilinear or straight shape or profile, which has been generally adopted throughout the industry, and as a result are utilized in most DC electric motors.
Due to the design of DC or AC electric motors, the brushes are in continuous physical contact with the commutator during the operation of the motor. In addition, due to the switching of the electrical currents supplied by the brushes to the commutator, an amount of electrical sparking/arcing is generated. Thus, the combination of the physical and electrical stress imparted to the brushes during operation of the motor creates an operating environment that typically causes the brushes to wear out well before the failure of the other components of the motor. As such, brush failure serves as one of the primary sources of failure in DC motors. Although the brushes may be replaced, allowing the motor to continue in service, such an endeavor is tedious, time consuming, and costly.
To overcome the problem of reduced electric motor operating life due to brush wear, attempts have been made to extend the physical length of the brush so that the brushes can operate for a longer period of time. However, electric motors are generally incorporated into an existing assembly of electromechanical components that have been previously designed to have only enough area to accommodate motors that utilize standard brush lengths. Although, the physical arrangement of the electromechanical components surrounding the motor may be revised to accommodate longer length brushes, other design constraints associated with the overall assembly forming the completed device may also be impacted. Thus, a redesign of a significant portion of the completed product or device may be required to accommodate longer length rectilinear brushes.
Furthermore, as curvilinear brushes wear during the operation of the motor unit, the brushes move within corresponding brush retainers, and as such, they are subject to stiction (static friction) or frictional forces that develop between the surfaces of the brush and the surfaces of the brush retainer upon which the brush is carried or guided. As such, stiction or frictional forces that resist the movement of the brush within the brush retainer cause the brush to stutter or skip as it moves toward the commutator as the brush wears during the operation of the motor unit. The stuttering and skipping that is imparted to the movement of the brush results in additional electrical sparking and/or arcing at the interface between the brush and the commutator. Unfortunately, however such sparking and/or arcing exacerbates the wear of the brushes, and thus prematurely reduces their operating life.
Therefore, there is a need for a brush retainer liner that reduces or eliminates the stiction or frictional forces between the brush and the surfaces of the brush retainer that contact the brush as it wears. In addition, there is a need for a curvilinear brush liner for a curvilinear brush retainer that reduces stiction or frictional forces about one or more surfaces of the brush that contacts the brush retainer.